<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        const url='http://localhost:3000';
        const data={username:'格格'};
        const myHeaders = new Headers({
            'X-Custom-Header':'XXX'
        })
        fetch(url,{
            method:'POST',
            body:JSON.stringify(data),
            headers:myHeaders,
            mode:'cors'
        })
        .then(res=>res.json())
        .then(res=>{
            console.log(JSON.parse(res.postData));
        })
    </script>
</body>
</html>